Composite polysulfide propellants containing additives for producing extremely fast burning



Unite States Patent ()fiice Patented Oct. 4, 1966 3,276,926 COMPOSITEPOLYSULFIDE PROPELILANTS CON- TAINING ADDITIVES FOR PRODUCING EX-TREMELY FAST BURNING John H. Robson III, 206A Lauritsen. China Lake,Calif. No Drawing. Filed Jan. 8, 1953, Ser. No. 330,365 1 Claim. (Cl.14919) The invention described herein may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

This invention relates to fast burning solid propellants and the methodfor making them; more particularly it relates to propellants to which acertain type additive has been added to increase their burning rate.

Various applications of propellants make it necessary to modify thepropellant to increase the burning rate. Typical applications are thosewithin a great thrust must be produced in a short time, such as bazookarockets and other missiles which reach their target shortly afterrelease. Another application of fast burning propellants is their use toincrease power output in motors o erating at low chamber pressures.

Various expedients have been used in the past to increase the burningrate of propellants. One such expedient is the use of hollow core grainsto obtain larger burning surfaces. This method has the disadvantage thatit necessitates an increase in the ratio of motor size to weight.Various additives have been used in the past but have beenunsatisfactory for various reasons.

It is therefore an object of this invention to provide propellants whichhave fast burning rates.

It is another object of this invention to provide additives forproducing propellants with fast burning rates which do not seriouslydetract from other necessary properties of the propellant.

It is still another object of this invention to provide a method forproducing fast burning propellants which is relatively inexpensive andsimple in application.

It has been found that the above and other objects can be accomplishedand the enumerated difiiculties overcome by the addition to propellantsof temperature sensitive high explosives, that is, high explosivessubject to detonation or explosion within a temperature range of about100 C. to about 400 C. The range of the particle size of the additive iscritical and is from about 20 to about 300 mesh. Examples of theseadditives are percholo'rate salts for example, the compoundshydroxylamine percholorate, hydrazine mono-perchlorate and semicarbazideperchlorate. Other examples of additives are lead azide, lead styphnate,heavy metal picrates and cobalt-azide-perchlorate complexes.

The above perchlorate additives may be prepared by two general methods.One method comprises treating the free amine in a suitable solvent withone equivalent of 70% perchlorate acid, followed by removal of Water andsolvent by distillation at reduced pressure and recrystallization of thesalt so obtained in a suitable solvent. Another method includes treatingthe hydrochloride or sulfate salt of the desired amine in absoluteethanol with an alcoholic solution of barium perchlorate, followed byremoval of the insoluable barium salt by filtration, concentration ofthe filtrate at reduced pressure and recrystallization of the salt soobtained in a suitable solvent.

The additives are incorporated in the fluid propellant at roomtemperature, and after thorough mixing this mixture is cast intosuitable containers and then conditioned at the appropriate temperatureto effect curing of the propellant (i.e. set to a solid). The additivesmay also be incorporated in double base propellants of either solvent orsolvent'less type, prior to rolling and extrusion of the gram.

The mechanism of the burning rate increase produced by the additive isbelieved to be due to a cratering effect on the burning propellantsurface caused by the violent decomposition of the additive atrelatively low temperatures in the solid phase of the propellant. Thiseffect is achieved by using coarse particles of additive in amounts of 5to 60% of the total propellant weight. Thus this method of increasingburning rates is not limited to any one type of solid propellant and maybe induced by any additive having physical and chemical propertiesmaking it susceptible to the catering effect.

The invention is illustrated by the following examples but is notlimited thereby:

EXAMPLE I In the following example the hydroxylamine perchlorate usedwas made by reacting hydroxylamine hydrochloride with barium perchloratein absolute ethanol and recovering the product by crystallization.

The propellant composition was prepared by thoroughly mixing 30.0 gramsof Thiokol LP-3, 65.0 grams of potassium perchlorate (ground and sievedsuch that passed a l00-mesh but not a 325-mesh screen, and 30% passed a325-mesh screen), 2.0 grams of p-quinone dioxime, 1.0 gram of diphenylguanidine, and 5.0 grams of hydroxylamine perchlorate of 100-200 meshsize. The above ingredient were mixed in the order given, at roomtemperature. After casting the mix in drinking straws by means of asuitable pressure casting device, the strands were conditioned 18 hoursat C.

Strands prepared in the above manner were found to burn very rapidly at1000 p.s.i. whereas strands of the same formulation from which thehydroxylamine perchlorate additive was omitted were found to have aburning rate at 1000 p.s.i. of only 1.06 inches per second.

EXAMPLE II Hydrazine perchlorate was prepared by reacting hydrazinehydrochloride with barium perchlorate. The propellant compositions wasprepared by thoroughly mixing 30 grams of Paraplex P-lO, 50 grams of-200 mesh hydrazine perchlorate and 40 grams of potassium perchlorate.Strands of this propellant were found to burn at 2.31 inches per secondat 1000 p.s.i., whereas the same size strands of a similar formulationat which the hydrazine perchlorate was entirely replaced by an equalweight of potassium perchlorate burned at only 1.27 inches per second at1000 p.s.i.

EXAMPLE III A propellant composition was prepared by thoroughly mixing30 grams of Paraplex P-10, 35 grams of 100-200 e) mesh hydrazineperchlorate and 35 grams of ammonium perchlorate. Strands of thispropellant were found to burn at 1.45 inches per second, whereas thesame size strands of similar formulation in which the hydrazineperchlorate was entirely replaced by an equal weight of ammoniumperchlorate burned at only 0.28 inch per second at 1000 p.s.i.

EXAMPLE IV Semicarbazide perchlorate was prepared by mixing, withstirring, solution A containing 44.6 grams of semicarbazidehydrochloride in 400 'cc. of water and solution B containing 82.8 gramsof silver perchlorate in 200 grams of water. The resulting solution wasfiltered to remove silver chloride and the filtrate concentrated undervacuum to yield a damp crystalline solid. This was dissolved in theminimum amount of hot methanol and recrystallized by adding six volumesof ethylene chloride. Filtration and vacuum drying yielded the desiredproduct. The propellent mixture was prepared by thoroughly mixing 30grams of Paraplex P-lO, 15 grams of 4080 mesh semicarbazide perchlorateand 55 grams of ammonium perchlorate. Strands of this propellant werefound to burn at 0.35 inch per second at 1800 p.s.i., whereas the samesize strands of a similar formulation in which the semicarbazideperchlorate was entirely replaced by an equal weight of ammoniumperchlorate burned at 0.32 inch per second at 1800 p.s.i. The Sigmoidrate-pressure curve showed conclusively that the semi-carbazideperchlorate had a rate-increasing effect similar to that of hydrazineperchlorate.

As the above results shown, the presence of the additives of thisinvention in a propellant increases the burning rate from two to eightfold that of the propellant alone. Other additives which may be used arethe N-alkyl substituted hydroxylamine perchlorates, the N-alkylsubstituted hydrazine perch'lorates and N-alkyl substitutedsemicarbazide perchlorates. In double base type propellants where it isnot necessary to maintain a high oxygen balance, any other temperaturesensitive high explosive such as lead azide, lead styphnate, heavy metalpicrates or cobalt-azideerchlorate complexes may be used to produce theburning rate increase effect.

In the illustrative examples the additives were incorporated in thepropellants in amounts of to 60% by weight that of the total weight ofthe propellant, however, varying amounts of additive may be useddepending upon the propellant being used and the burning rate required.Although the propellant used in illustrating the invention were aThiokol LP-3 type propellant and a Paraplex P- propellant, the additivesmay be used to increase the burning rate of other propellants, as theincrease in burning rate is due to the thermal decompositioncharacteristics of the additives, namely, the rapid decomposition orexplosion of large particles of additive at relatively low temperatures.Mixtures of the various additives of the invention may be used ratherthan a single additive.

The Thiokol LP-3 and Paraplex P-10, referred to in the above examples,are well known elastomers.

A bulletin published November 21, 1952 by the Thiokol Corporation andentitled Thiokol Liquid Polymer LP-3, disloses that Thiokol LP-3 is aliquid polysulfide polymer having a low molecular Weight.

Unconverted Thiokol LP-S is essentially a difunctional mercaptan madefrom 98 mole percent of bis(2-chloroethyl) formal and 2 mole percent oftrichloropropane, a crosslinking agent. The polymer segments arecomposed of a number of formal groups linked by sulfur bonds and areterminated by mercaptan groups; side mercaptan groups occur occasionallyin the chain of repeating formal units and some chain segments arecrosslinked at various points. The average structure of Thiokol LP-3 maybe represented as follows:

The following are a number of the more important typical physicalproperties of the unconverted liquid polymer:

Physical state Mobile liquid. Color Clear, amber. Specific gravity 20/20 C 1.27 Viscosity 25 C., centipoises 700-1200. Average molecularweight 1000 Pour point 15 F. Flash point (open cup) 418 F.

Fire point (open cup) 465 F.

pH (water extract) 6.0-8.0 Moisture content 0.1% max. StabilityUnlimited (over 3 years).

A booklet published August 8, 1947 by Resinous Products and ChemicalCompany of Philadelphia, Pennsylvania, and entitled Paraplex forLaminating and Casting Applications, discloses that Paraplex P10 is astyrene solution of unsaturated polyester or alkyd resins consisting of50% by weight of styrene and 50% by weight of polyester. It is areactive, thermosetting resin which, under the influence of heat andperoxides, will polymerize to an inert, insoluble, infusible product.Paraplex P-lO contains no water and pre-drying operations are notnecessary. It is percent reactive and cures by polymerization (orcopolymerization) rather than by condensation as in the case ofphenolics, and, as a result, no volatile byproducts are split out duringthe reaction. In its final form, Paraplex Pl0 is an extremely flexiblecomposition.

As stated above, Paraplex P-10 is reactive. Even at room temperature, itwill gel eventually and, given infinite time, could polymerize to itsultimate thermoset form. However, there are several ways of acceleratingthis reaction. First, direct or infra-red heat, or ultra-violetradiation can be used to accelerate the rate of action. Secondly,peroxide catalysts can be used, just as they are used in conventionalvinyl monomer polymerizations- Benzoyl peroxide (in the form of LupercoATC, a benzoyl peroxide supplied in paste form with an equal weight oftricresyle phosphate) tertiary butyl perbenzoate, and others, used inconcentrations of 1 to 2 percent on the weight of the Paraplex, havebeen found suitable. Actually, a combination of heat and peroxidegenerally is used in practice. The curing is generally accepted as atrue copolymerization, and the final product is a homogeneouscomposition anda three dimensional polymer. In curing, the resin firsttends to thin as it reaches curing temperature, then gels to a veryweak, soft mass and; on subsequent heating, cures to a firm composition,showing an appreciable volume reduction and a corresponding increase inspecific gravity during cure.

The physical properties of unpolymerized Paraplex P-10 are as follows:

Viscosity (cps.) 350550. Color Amber. Appearance Clear. Acid number Lessthan 2.

Odor Styrene. Spec. gravity .982.984. Refractive index 1.5115.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claim the invention maybe practiced otherwise than as specifically described.

What is claimed is:

A propellent composition consisting of about 65 parts by weight ofpotassium perchlorate, about 2 parts by 5 6 Weight of p-quinone dioxime,about 1 part by weight of FOREIGN PATENTS diphenyl guanidine, about 5parts by Weight of hydroxyl- 523,732 4/1921 France amine perchlorate andabout 30 parts by Weight of a polysulfide polymer having the averagestructure OTHER REFERENCES 5 Audrieth: The Chemistry of Hydrazine, JohnWiley &

HS (CZHQOCHZ"OC2H4'S' S)6 Sons, New York City 1951 pages 177, 189.

2 4 2 2 4 McLarren: Automotive and Aviation Industries,

August 15, 194-6, pages 20-23, inclusive, and 76. References Cited bythe Examiner UNITED STATES PATENTS 1Q BENJAMIN R. PADGETT, AclirzgPrimary Examiner. 2,406,572 8/1946 VOg1 WILLIAM G. WILES, ROBERT L.CAMPBELL, 2,479,470 8/1949 Carr 52.5 Emmmm' 2,479,828 8/ 1949 Geckler.LEON D. ROSDOL, Assistant Examiner.

